Preparation of glycol carboxyethylmethylphosphinate

Abstract

The invention relates to a process of preparing glycol carboxyethylmethylphosphinate, which comprises a) reacting elemental yellow phosphorus with methyl chloride in the presence of an alkali or alkaline earth metal hydroxide to form a mixture which includes the alkali and/or alkaline earth metal salts of methylphosphonous, phosphorous and hypophosphorous acids as main constituents, b) esterifying the methylphosphonous acid from the mixture obtained by a), c) removing the methylphosphonous ester from the mixture, d) adding the thus obtained methylphosphonous ester to an acrylic ester, e) hydrolyzing the diester thus obtained, f) esterifying the resulting carboxyethylmethylphosphinic acid with ethylene glycol directly to the glycol carboxyethylmethylphosphinate. The invention also relates to the use of the glycol carboxyethylmethylphosphinates prepared according to the invention as reactive flame retardants for polymers.

1. A process of preparing glycol carboxyethylmethylphosphinate, comprising the steps of:
 a) reacting elemental yellow phosphorus with methyl chloride in the presence of an alkali or alkaline earth metal hydroxide to form a mixture which includes the alkali and/or alkaline earth metal salts of methylphosphonous, phosphorous and hypophosphorous acids as main constituents,  
 b) esterifying the methylphosphonous acid from the mixture obtained by a),  
 c) removing the methylphosphonous ester from the mixture,  
 d) adding the thus obtained methylphosphonous ester to an acrylic ester,  
 e) hydrolyzing the diester thus obtained,  
 f) esterifying the resulting carboxyethylmethylphosphinic acid with ethylene glycol directly to the glycol carboxyethylmethylphosphinate.  
 
     
     
       2. The process of  claim 1 , wherein step a) is carried out in an organic solvent. 
     
     
       3. The process of  claim 2 , wherein the organic solvent is selected from the group consisting of straight-chain or branched alkanes, alkyl-substituted aromatic solvents, water-immiscible or only partly water-miscible alcohols and ethers used alone or combined with each other. 
     
     
       4. The process of  claim 2 , wherein the organic solvent used is toluene, alone or in combination with alcohols. 
     
     
       5. The process of  claim 1 , wherein step a) is carried out in the presence of a phase transfer catalyst. 
     
     
       6. The process of  claim 5 , wherein the phase transfer catalyst comprises tetraalkylphosphonium halides, triphenylalkylphosphonium halides or tetraorganoammonium halides. 
     
     
       7. The process of  claim 1 , wherein step a) is carried out at a temperature in the range from −20 to +60° C. 
     
     
       8. The process of  claim 1 , wherein step a) is carried out at a temperature in the range from 0 to 30° C. 
     
     
       9. The process of  claim 1 , wherein step a) is carried out under a pressure in the range from 0 to 10 bar. 
     
     
       10. The process of  claim 1 , wherein step a) further comprises suspending the yellow phosphorus in a solvent or solvent mixture and then reacting with an alkyl halide and a compound of the formula MOH or M′(OH) 2  or mixtures thereof, where M is an alkali metal and M′ is an alkaline earth metal. 
     
     
       11. The process of  claim 10 , wherein the yellow phosphorus and the methyl chloride are reacted with each other in a molar ratio in the range from 1:1 to 1:3, the molar ratio of yellow phosphorus to compound of the formula MOH or M′(OH) 1  being in the range from 1:1 to 1:5. 
     
     
       12. The process of  claim 1 , wherein step b) further comprises esterifying the methyl phosphonous acid with an alcohol in a mixture. 
     
     
       13. The process of  claim 1 , wherein step c) further comprises removing the methanephosphonous ester by distillation. 
     
     
       14. The process of  claim 1 , wherein step d) is effected in the presence of a catalyst. 
     
     
       15. The process of  claim 14 , wherein the catalyst is a basic catalyst. 
     
     
       16. The process of  claim 14 , wherein the basic catalyst is an alkali or alkaline earth metal alkoxide. 
     
     
       17. The process of  claim 1 , wherein the acrylic ester is methyl acrylate, butyl acrylate or ethylhexyl acrylate. 
     
     
       18. A flame retardant polymer comprising a polymer and glycol carboxyethylmethylphosphinate prepared by the process of  claim 1 . 
     
     
       19. A reactive flame retardant for a thermoplastic polymer comprising the glycol carboxyethylmethylphosphinate prepared by the process of  claim 1 , wherein the thermoplastic polymer is selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate or polyamide. 
     
     
       20. A process for making a flame retardant polymer comprising the step of adding to the polymer the glycol carboxyethylmethylphosphinate prepared by the process of  claim 1 . 
     
     
       21. The process of  claim 20 , wherein the polymer is selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate or polyamide.